Going Backward 

Organisms usually move upward on the evolutionary ladder, losing some traits to gain better ones. 

And then there are those who move backward. 

A new study has found that some wild tomatoes from the Galápagos Islands are undergoing a possible “reverse evolution,” de-evolving to a primitive genetic state by recreating a toxic molecular cocktail that serves as a defense mechanism, and one that has not been seen in millions of years. 

“It’s not something we usually expect,” lead study author Adam Jozwiak said in a statement. “But here it is, happening in real time, on a volcanic island.” 

Nightshade plants, like tomatoes, potatoes, and eggplants, produce bitter-tasting molecules known as alkaloids to protect themselves from fungi, insects, and larger animals. However, too many alkaloids can make the plants toxic and dangerous for humans, explained New Atlas. 

Researchers were studying crops on the Galápagos Islands to understand how to control alkaloid synthesis when they noticed the tomatoes’ unique behavior.  

Analyzing more than 30 tomato samples collected from different parts of the archipelago, the team found that those from the eastern islands produced the same alkaloids found in modern cultivated tomatoes.  

Meanwhile, the samples from the western islands were producing the “wrong” kind: A version with the molecular fingerprint of eggplant relatives from millions of years ago. 

The difference is in how atoms are arranged in three-dimensional space, namely, stereochemistry. Two molecules can have the same atoms but behave differently depending on how the atoms are arranged. 

To understand the difference between the eastern and western samples, researchers analyzed the enzymes that assemble these alkaloid molecules. By changing just four amino acids in one enzyme, they could reverse the molecule’s structure from modern to ancestral. 

To reach this conclusion, they synthesized the genes coding for these enzymes in the lab and then inserted them into tobacco plants, which immediately started producing the old structure. 

Through DNA modeling, the team explained the connection between the tomatoes’ behavior and geography. Crops on the eastern, older islands make modern alkaloids as the soil is more stable and biologically diverse. In contrast, those on the western islands adopted the old structure as the soil is less developed there. 

“It could be that the ancestral molecule provides better defense in the harsher western conditions,” Jozwiak said. 

Researchers say that evolution is traditionally understood as a one-way street. While some species can regain similar characteristics to those of their ancestors, they rarely do so following the exact same genetic pathways. 

As a result, the concept of “reverse evolution” is controversial: “Some people don’t believe in this,” Jozwiak said. “But the genetic and chemical evidence points to a return to an ancestral state. The mechanism is there. It happened.”